There's been multiple questions about this lately. Will be a little long, but hopefully this info will help get some over the hump to give it a try. I've horizontally and vertically bi-amped at least 20 different configurations(lost count) in recent years with varying levels of success, but each time improving with experience. Being a classic Infinity fan, most were with Infinity speakers including Kappa 8,9, Ren 90 and RS2B ending up with IRS Betas. Bi-Amping with the Betas and 2B's were easiest and most successful as both had a Servo or Bass Eq to adjust gain for the low frequencies for ideal match.
Pre-Amps used were Carver C19, Sunfire Tube, Mac C70, C1100 and currently Ayon.
Amps used were several different Carver/Sunfire/Lightstar combos, then McIntosh 275 single and monos with Bryston 7B's for lows; later replacing with MC2301's and Legacy I-V2 all leading to my current Analysis Orions which are actually Tri-Amped using MC901's and Speaker Power Monos on bass panels for time alignment and frequency/level adjustment in a full active set up using the MC901's internal crossover as well. It is true that you tweak until you figure it out, but when you get to your sweet spot it stays pretty consistent.
Simple rule of thumb is to have double the power to your lows as your mids/highs. McIntosh demonstrates this with the 451 and 901. I'll say upfront that the 901's have bested every combo in every way, but they should for the price. The MC275's were one of my favorite for Bi-Amping. They sound smooth and sweet and reduce the chance of overpowering your mids/highs vs some other options. You can save some money going with lower cost but high quality SS A/B or Class D amp/monos for your lows instead of the 611's and apply those funds to an active crossover or even one of the few Pre-Amp options out there with adjustable pre-amp outputs.
Having owned all the Mac tube amps listed above, I can share first hand that heat has never been an issue. I live in the Southeast and listen all I want in the summer months in a listening room above my garage which is a room more challenging to cool with no issue. It's not even a concern.
You will need additional cables and interconnects. Use inexpensive options until you dial in, then upgrade as you want/need. The Mac 451/901's do save you a set of power cords and interconnects with their configuration and really make it easy. They bring a simpler, seamless experience if you are willing to invest in them. Mac is on to something, I wouldn't be surprised if we see a 75/150 option coming at some point.